1. Field of the Invention
This invention relates to a two-stage detection noncontact positioning apparatus which is capable of focusing on a surface of an object in a noncontacting and highly accurate manner.
2. Description of the Prior Art
It is a technically very difficult problem to achieve optical focusing in a noncontacting manner upon objects of various size, shape, and physical properties. As a focusing technique generally practiced heretofore, there is an image processing technique using a computer.
Such an image processing technique, however, has difficulties in that it requires a large-scale apparatus, and is slow in performing focusing operations because of image scanning to be executed therein, with insufficient reliability due to susceptibility to influence of luminance distribution.
To overcome these difficulties, the present inventor previously proposed a noncontact positioning apparatus (Japanese Laid-open Patent Application (Kokai) No. 62-75411 corresponding to U.S. Pat. No. 4,843,228 and EP Publication No. 0273 717 B1) which utilizes a laser beam. The proposed noncontact positioning apparatus comprises a laser beam-emitting mechanism for emitting a laser beam as a measuring beam, an optical mechanism having mirror means for reflecting the measuring beam in a direction parallel to an optical axis, an objective lens for refracting the measuring beam toward an object and for refracting again the measuring beam reflected from the object, and a focusing lens for causing the measuring beam reflected from the object and refracted by the objective lens to focus on a position located on the optical axis, a light position-detecting mechanism of a split-in-two type for receiving the measuring beam passed through the focusing lens to deliver a position signal, and a focusing mechanism responsive to the position signal from the light position-detecting mechanism for moving at least one of the object and the objective lens to thereby automatically focus the measuring beam on a surface of the object.